Heated laser package with increased efficiency for optical transmitter systems

ABSTRACT

A heated laser package generally includes a laser diode, a heating resistor and a transistor in a single laser package. The heating resistor and transistor form a heating circuit and may be located on a submount adjacent to the laser diode. The transistor is configured to control the drive current to the heating resistor and any additional heat generated by the transistor may contribute to the heating of the laser diode and thus increase the thermal efficiency of the system. The heated laser package may be used in a temperature controlled multi-channel transmitter optical subassembly (TOSA), which may be used in a multi-channel optical transceiver. The optical transceiver may be used in a wavelength division multiplexed (WDM) optical system, for example, in an optical line terminal (OLT) in a WDM passive optical network (PON).

TECHNICAL FIELD

The present disclosure relates to optical transmitters and more particularly, to a heated laser package with increased efficiency for use in a multi-channel transmitter optical subassembly (TOSA) providing thermal control.

BACKGROUND INFORMATION

Optical communications networks, at one time, were generally “point to point” type networks including a transmitter and a receiver connected by an optical fiber. Such networks are relatively easy to construct but deploy many fibers to connect multiple users. As the number of subscribers connected to the network increases and the fiber count increases rapidly, deploying and managing many fibers becomes complex and expensive.

A passive optical network (PON) addresses this problem by using a single “trunk” fiber from a transmitting end of the network, such as an optical line terminal (OLT), to a remote branching point, which may be up to 20 km or more. One challenge in developing such a PON is utilizing the capacity in the trunk fiber efficiently in order to transmit the maximum possible amount of information on the trunk fiber. Fiber optic communications networks may increase the amount of information carried on a single optical fiber by multiplexing different optical signals on different wavelengths using wavelength division multiplexing (WDM). In a WDM-PON, for example, the single trunk fiber carries optical signals at multiple channel wavelengths to and from the optical branching point and the branching point provides a simple routing function by directing signals of different wavelengths to and from individual subscribers. In this case, each subscriber may be assigned one or more of the channel wavelengths on which to send and/or receive data.

To transmit and receive optical signals over multiple channel wavelengths, the OLT in a WDM-PON may include a multi-channel transmitter optical subassembly (TOSA) and a multi-channel receiver optical subassembly (ROSA). One example of a TOSA includes an array of lasers optically coupled to an arrayed waveguide grating (AWG) to combine multiple optical signals at multiple channel wavelengths. To provide the different channel wavelengths, tunable lasers may be used in the multi-channel TOSA and the wavelengths emitted by the tunable lasers change with changes in temperature. The desired accuracy or precision of the wavelengths in a WDM-PON often depends on the number and spacing of the channel wavelengths and may be controlled in the TOSA by controlling temperature. In a 100 G dense WDM (DWDM) system, for example, the temperature may need to be controlled within ±0.5° C. to maintain a wavelength precision of ±0.5 nm and the temperature range may need to be greater than 4° C. to provide the desired wavelength yield of the laser diodes.

One challenge with such OLT transceiver modules is providing adequate temperature control of the laser array in a relatively small space and with relatively low power consumption. One way to control temperature of the individual laser diodes in a laser array is to use individual temperature control devices, such as thermoelectric (TEC) coolers, and temperature monitors (e.g., thermistors) for each of the respective laser diodes to provide a closed loop temperature control for each of the lasers based on a monitored temperature. To support 16 channels in a TOSA, for example, would require 16 TEC's, 16 thermistors, 32 ports for the thermistors and circuitry for controlling each of these components. Such a closed loop system requires a more complicated circuit design and higher cost and may not fit within a smaller form factor for the OLT transceiver module. Another challenge with heating and temperature control for thermally tuned lasers is operating within a power budget for the OLT module.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages will be better understood by reading the following detailed description, taken together with the drawings wherein:

FIG. 1 is a functional block diagram of a wavelength division multiplexed (WDM) passive optical network (PON) including at least one multi-channel optical transceiver, consistent with embodiments of the present disclosure.

FIG. 2 is an exploded view of a multi-channel optical transceiver including a temperature controlled multi-channel TOSA, consistent with an embodiment of the present disclosure.

FIG. 3 is a top view inside the multi-channel optical transceiver shown in FIG. 2.

FIG. 4 is an end perspective view of one embodiment of a temperature controlled multi-channel TOSA.

FIG. 5 is a side perspective view of the temperature controlled multi-channel TOSA shown in FIG. 4.

FIG. 6 is a top view of one embodiment of a heated laser package for use in a temperature controlled multi-channel TOSA.

FIG. 7 is a diagrammatic view of a temperature controlled multi-channel TOSA, consistent with an embodiment of the present disclosure.

FIG. 7A is a chart illustrating the change in wavelength of each of the lasers in the temperature controlled multi-channel TOSA as a function of temperature.

FIG. 8 is a block diagram of a local temperature control circuit for a heated laser package consistent with an embodiment of the present disclosure.

FIG. 9 illustrates a flowchart of operations of another example embodiment consistent with the present disclosure.

DETAILED DESCRIPTION

A heated laser package, consistent with embodiments described herein, generally includes a laser diode, a heating resistor and a transistor in a single laser package. The heating resistor and transistor form a heating circuit and may be located on a submount adjacent to the laser diode. The transistor is configured to control the drive current to the heating resistor and any additional heat generated by the transistor may contribute to the heating of the laser diode and thus increase the thermal efficiency of the system.

The heated laser package may be used in a temperature controlled multi-channel transmitter optical subassembly (TOSA), which may be used in a multi-channel optical transceiver. The temperature controlled multi-channel TOSA generally includes an array of lasers optically coupled to an optical multiplexer, such as an arrayed waveguide grating (AWG), to combine multiple optical signals at different channel wavelengths. The lasers may be thermally tuned to the channel wavelengths by establishing a global temperature for the array of lasers and separately raising local temperatures of individual lasers. A temperature control device, such as a TEC cooler coupled to the laser array, may provide the global temperature, and individual heaters, such as resistors and transistors adjacent to respective lasers, may provide the local temperatures. The optical transceiver may be used in a wavelength division multiplexed (WDM) optical system, for example, in an optical line terminal (OLT) in a WDM passive optical network (PON).

As used herein, a “laser package” refers to a laser diode packaged with other components such as a submount, a monitor photodiode, a thermal shield, and/or optics. As used herein, “channel wavelengths” refer to the wavelengths associated with optical channels and may include a specified wavelength band around a center wavelength. In one example, the channel wavelengths may be defined by an International Telecommunication (ITU) standard such as the ITU-T dense wavelength division multiplexing (DWDM) grid. As used herein, “tuning to a channel wavelength” refers to adjusting a laser output such that the emitted laser light includes the channel wavelength. The term “coupled” as used herein refers to any connection, coupling, link or the like and “optically coupled” refers to coupling such that light from one element is imparted to another element. Such “coupled” devices are not necessarily directly connected to one another and may be separated by intermediate components or devices that may manipulate or modify such signals. As used herein, “thermally coupled” refers to a direct or indirect connection or contact between two components resulting in heat being conducted from one component to the other component. As used herein, “thermally isolated” refers to an arrangement where heat is prevented from being conducted to the isolated component from an external environment. In a thermally isolated multi-channel TOSA, for example, heat external to the TOSA is prevented from being conducted to one or more components in the TOSA. As used herein, “thermally shielded” refers to an arrangement that prevents heat from being transferred by convection or radiation to the shielded component. Thermally isolated and thermally shielded do not necessarily require an arrangement to prevent all heat from being conducted or transferred.

Referring to FIG. 1, a WDM-PON 100 including one or more multi-channel optical transceivers 102 a, 102 b, consistent with embodiments of the present disclosure, is shown and described. The WDM-PON 100 provides a point-to-multipoint optical network architecture using a WDM system. According to one embodiment of the WDM-PON 100, at least one optical line terminal (OLT) 110 may be coupled to a plurality of optical networking terminals (ONTs) or optical networking units (ONUs) 112-1 to 112-n via optical fibers, waveguides, and/or paths 114, 115-1 to 115-n. Although the OLT 110 includes two multi-channel optical transceivers 102 a, 102 b in the illustrated embodiment, the OLT 110 may include one or more multi-channel optical transceivers.

The OLT 110 may be located at a central office of the WDM-PON 100, and the ONUs 112-1 to 112-n may be located in homes, businesses or other types of subscriber location or premises. A branching point 113 (e.g., a remote node) couples a trunk optical path 114 to the separate optical paths 115-1 to 115-n to the ONUs 112-1 to 112-n at the respective subscriber locations. The branching point 113 may include one or more passive coupling devices such as a splitter or optical multiplexer/demultiplexer. In one example, the ONUs 112-1 to 112-n may be located about 20 km or less from the OLT 110.

The WDM-PON 100 may also include additional nodes or network devices, such as Ethernet PON (EPON) or Gigabit PON (GPON) nodes or devices, coupled between the branching point 113 and ONUs 112-1 to 112-n at different locations or premises. One application of the WDM-PON 100 is to provide fiber-to-the-home (FTTH) or fiber-to-the-premises (FTTP) capable of delivering voice, data, and/or video services across a common platform. In this application, the central office may be coupled to one or more sources or networks providing the voice, data and/or video.

In the WDM-PON 100, different ONUs 112-1 to 112-n may be assigned different channel wavelengths for transmitting and receiving optical signals. In one embodiment, the WDM-PON 100 may use different wavelength bands for transmission of downstream and upstream optical signals relative to the OLT 110 to avoid interference between the received signal and back reflected transmission signal on the same fiber. For example, the L-band (e.g., about 1565 to 1625 nm) may be used for downstream transmissions from the OLT 110 and the C-band (e.g., about 1530 to 1565 nm) may be used for upstream transmissions to the OLT 110. The upstream and/or downstream channel wavelengths may generally correspond to the ITU grid. In one example, the upstream wavelengths may be aligned with the 100 GHz ITU grid and the downstream wavelengths may be slightly offset from the 100 GHz ITU grid.

The ONUs 112-1 to 112-n may thus be assigned different channel wavelengths within the L-band and within the C-band. Transceivers or receivers located within the ONUs 112-1 to 112-n may be configured to receive an optical signal on at least one channel wavelength in the L-band (e.g., λ_(L1), λ_(L2), . . . λ_(Ln)). Transceivers or transmitters located within the ONUs 112-1 to 112-n may be configured to transmit an optical signal on at least one channel wavelength in the C-band (e.g., λ_(C1), λ_(C2), . . . λ_(Cn)). Other wavelengths and wavelength bands are also within the scope of the system and method described herein.

The branching point 113 may demultiplex a downstream WDM optical signal (e.g., λ_(L1), λ_(L2), . . . λ_(Ln)) from the OLT 110 for transmission of the separate channel wavelengths to the respective ONUs 112-1 to 112-n. Alternatively, the branching point 113 may provide the downstream WDM optical signal to each of the ONUs 112-1 to 112-n and each of the ONUs 112-1 to 112-n separates and processes the assigned optical channel wavelength. The individual optical signals may be encrypted to prevent eavesdropping on optical channels not assigned to a particular ONU. The branching point 113 also combines or multiplexes the upstream optical signals from the respective ONUs 112-1 to 112-n for transmission as an upstream WDM optical signal (e.g., λ_(C1), λ₂, . . . λ_(Cn)) over the trunk optical path 114 to the OLT 110.

One embodiment of the ONU 112-1 includes a laser 116, such as a laser diode, for transmitting an optical signal at the assigned upstream channel wavelength (λ_(C1)) and a photodetector 118, such as a photodiode, for receiving an optical signal at the assigned downstream channel wavelength (λ_(L1)). The laser 116 may include a tunable laser configured to be tuned to the assigned channel wavelength, and more specifically, may be provided as a heated laser package capable of thermally tuning the laser as described herein. This embodiment of the ONU 112-1 may also include a diplexer 117 coupled to the laser 116 and the photodetector 118 and a C+L band filter 119 coupled to the diplexer 117, which allow the L-band channel wavelength (λ_(L1)) to be received by the ONU 112-1 and the C-band channel wavelength (λ_(C1)) to be transmitted by the ONU 112-1.

The OLT 110 may be configured to generate multiple optical signals at different channel wavelengths (e.g., λ_(L1), λ_(L2), . . . λ_(Ln)) and to combine the optical signals into the downstream WDM optical signal carried on the trunk optical fiber or path 114. Each of the OLT multi-channel optical transceivers 102 a, 102 b may include a multi-channel transmitter optical subassembly (TOSA) 120 for generating and combining the optical signals at the multiple channel wavelengths. The OLT 110 may also be configured to separate optical signals at different channel wavelengths (e.g., λ_(C1), λ_(C2) . . . λ_(Cn)) from an upstream WDM optical signal carried on the trunk path 114 and to receive the separated optical signals. Each of the OLT multi-channel optical transceivers 102 a, 102 b may thus include a multi-channel receiver optical subassembly (ROSA) 130 for separating and receiving the optical signals at multiple channel wavelengths.

One embodiment of the multi-channel TOSA 120 includes an array of lasers 122, such as laser diodes, which may be modulated by respective RF data signals (TX_D1 to TX_Dm) to generate the respective optical signals. The lasers 122 may be modulated using various modulation techniques including external modulation and direct modulation. An optical multiplexer 124, such as an arrayed waveguide grating (AWG), combines the optical signals at the different respective downstream channel wavelengths (e.g., λ_(L1), λ_(L2), . . . λ_(Ln)). The TOSA 120 may also include a temperature control system for controlling temperature of the lasers 122 and the multiplexer 124 to maintain a desired wavelength precision or accuracy. As described in greater detail below, the lasers 122 may be provided as heated laser packages and may be tuned to the channel wavelengths by raising the local temperature of the individual lasers 122 above a global temperature based on calibration data associated with the laser diode and/or in response to monitored wavelengths. The lasers may also be thermally isolated and/or thermally shielded to facilitate temperature control, as described in greater detail below.

In some embodiments, the lasers 122 may be tunable lasers that generate the optical signals at the respective channel wavelengths. In other embodiments, the lasers 122 may generate optical signals over a band of channel wavelengths and filtering and/or multiplexing techniques may be used to produce the assigned channel wavelengths. Examples of optical transmitters including a laser array and AWG are disclosed in greater detail in U.S. patent application Ser. No. 13/543,310 (U.S. Patent Application Pub. No. 2013-0016971), U.S. patent application Ser. No. 13/357,130 (U.S. Patent Application Pub. No. 2013-0016977), and U.S. patent application Ser. No. 13/595,505 (U.S. Patent Application Pub. No. ______), all of which are fully incorporated herein by reference. In the illustrated embodiment, the OLT 110 further includes a multiplexer 104 for multiplexing the multiplexed optical signal from the multi-channel TOSA 120 in the multi-channel transceiver 102 a with a multiplexed optical signal from a multi-channel TOSA in the other multi-channel transceiver 102 b to produce the downstream aggregate WDM optical signal.

One embodiment of the multi-channel ROSA 130 includes a demultiplexer 132 for separating the respective upstream channel wavelengths (e.g., λ_(C1), λ_(C2), . . . . λ_(Cn)). An array of photodetectors 134, such as photodiodes, detects the optical signals at the respective separated upstream channel wavelengths and provides the received data signals (RX_D1 to RX_Dm). In the illustrated embodiment, the OLT 110 further includes a demultiplexer 106 for demultiplexing the upstream WDM optical signal into first and second WDM optical signals provided to the respective multi-channel ROSA in each of the transceivers 102 a, 102 b. The OLT 110 also includes a diplexer 108 between the trunk path 114 and the multiplexer 104 and the demultiplexer 106 such that the trunk path 114 carries both the upstream and the downstream channel wavelengths. The transceivers 102 a, 102 b may also include other components, such as laser drivers, transimpedance amplifiers (TIAs), and control interfaces, used for transmitting and receiving optical signals.

In one example, each of the multi-channel optical transceivers 102 a, 102 b may be configured to transmit and receive 16 channels such that the WDM-PON 100 supports 32 downstream L-band channel wavelengths and 32 upstream C-band channel wavelengths. One example of the WDM-PON 100 may operate at 1.25 Gbaud on-off keying as the modulation scheme. Other data rates and modulation schemes may also be used.

As mentioned above, the upstream and downstream channel wavelengths may span a range of channel wavelengths on the 100 GHz ITU grid. Each of the transceivers 102 a, 102 b, for example, may cover 16 channel wavelengths in the L-band for the TOSA and 16 channel wavelengths in the C-band for the ROSA such that the transceivers 102 a, 102 b together cover 32 channels. Thus, the multiplexer 104 may combine 16 channels from one transceiver 102 a with 16 channels from the other transceiver 102 b, and the demultiplexer 106 may separate a 32 channel WDM optical signal into two 16 channel WDM optical signals. To facilitate use of the multiplexer 104 and the demultiplexer 106, the range of channel wavelengths may skip channels in the middle of the range. According to one example of a multi-channel optical transceiver used in the WDM-PON 100, the desired wavelength precision or accuracy is ±0.05 nm and the desired operating temperature is between −5 and 70° C.

Referring to FIGS. 2 and 3, one embodiment of a multi-channel optical transceiver module 202 including a temperature controlled multi-channel TOSA 220 is shown and described in greater detail. As discussed above, multiple multi-channel transceiver modules may be used in an OLT of a WDM-PON to cover a desired channel range. The transceiver module 202 and the multi-channel TOSA 220 within the transceiver module 202 may thus be designed to have a relatively small form factor imposing spatial constraints. The multi-channel optical transceiver module 202 generally provides an optical input and output at one end 204 and electrical input and output at another end 206. The transceiver module 202 includes a transceiver housing 210 containing the thermally isolated multi-channel TOSA 220, a multi-channel ROSA 230, and a dual fiber type direct link adapter 250 directly linked to the TOSA 220 and the ROSA 230 for providing the optical input and output.

The dual fiber type direct link adapter 250 is coupled to the TOSA 220 and to the ROSA 230 with respective optical fibers 222, 232 to provide the direct link between the adapter 250 and both the TOSA 220 and the ROSA 230. The dual fiber type direct link adapter 250 is also configured to receive pluggable optical connectors, such as LC connectors (not shown), to connect the TOSA 220 and ROSA 230, respectively, to fiber optic cables (not shown). When the pluggable optical connectors are plugged into the dual fiber type direct link adapter 250, the adapter 250 establishes an optical coupling between the TOSA 220 and the ROSA 230 and the respective optical fibers in the fiber-optic cables, which carry the optical signals to and from the transceiver.

The temperature controlled multi-channel TOSA 220 includes an array of lasers (not shown in FIGS. 2 and 3) coupled to an AWG 225. A temperature control system, as will be described in greater detail below, controls the temperature of the individual lasers to provide a desired wavelength with a desired wavelength precision or accuracy. In one example, the temperature of each laser is maintained within ±0.5° C. in the operating range between −5 and 70° C. to maintain a wavelength precision or accuracy of about ±0.05 nm. The temperature control system may control the temperature by raising the local temperatures of individual lasers individually above a global temperature and adjusting the local temperatures based on calibration data associated with the laser diode and/or in response to monitored wavelengths associated with the lasers.

The transceiver module 202 may also include one or more printed circuit boards (PCBs) 208 coupled to the TOSA 220 and/or ROSA 230. The PCBs 208 may include circuitry and electronic components such as laser drivers, transimpedance amplifiers (TIAs), control interfaces, and temperature control circuitry. The TOSA 220 is coupled to conductive leads 224 for carrying the electronic signals including the data to be transmitted by the TOSA 220. The ROSA 230 is coupled to the conductive leads 234 for carrying the electronic signals including the data received by the ROSA 230.

A top housing portion 212 encloses the TOSA 220, the ROSA 230, the adapter 250, the optical fibers 222, 232, and other components within the housing 210. The transceiver housing 210 may have a width of less than about 55 mm, a length of less than about 130 mm, and a height of less than about 10 mm. More specifically, one example of a transceiver housing 210 may have a width of 54.6 mm, a length of 110 mm, and a height of about 9.8 mm. Within the transceiver module 202, the thermally isolated multi-channel TOSA 220 has a width, a height and length capable of fitting within the transceiver housing 210.

Referring to FIGS. 4 and 5, an embodiment of the temperature controlled multi-channel TOSA 220 is described in greater detail. This embodiment of the temperature controlled multi-channel TOSA 220 is also thermally isolated and thermally shielded to facilitate the temperature control. The temperature control system and method described herein may also be used in other embodiments of a multi-channel TOSA, for example, without thermal isolation and/or thermal shielding.

This embodiment of the temperature controlled multi-channel TOSA 220 includes an array of lasers 226-1 to 226-n (only laser 226-1 is shown in detail) optically coupled to the AWG 225. Each of the lasers 226-1 to 226-n in the array may be a distributed feedback (DFB) laser capable of altering lasing wavelengths in response to temperature changes and may be thermally shielded, as described in greater detail below. The lasers 226-1 to 226-n may be optically coupled to the AWG 225, for example, using low bending loss optical fibers (not shown). Each laser 226-1 may be provided as a heated laser package including, but not limited to, a laser diode chip mounted on a laser mounting structure or sub-mount. The heated laser package may also include a heating resistor and an associated transistor configured to control drive current to the heating resistor. Both the heating resistor and the transistor may be located in proximity to the laser diode, as will be described in greater detail below, such that heat generated from either or both components may be transferred to the laser diode providing for increased thermal efficiency. The heated laser package may further include optical components, such as a lens for optically coupling the laser light into a respective one of the optical fibers, and/or optoelectronic components, such as a monitor photodiode. The AWG 225 may include an AWG chip such as the type used for WDM, Coarse WDM (CWDM), or Dense (DWDM) multiplexing or demultiplexing.

In this embodiment, the array of lasers 226-1 to 226-n are supported on a laser array tray 240 and the AWG 225 is supported on an AWG tray 242. Both the laser array tray 240 and the AWG tray 242 may be thermally coupled to the same temperature control device 260 such that the temperature control device 260, the laser array tray 240 and the AWG tray 242 provide a temperature control system for the TOSA within a relatively small space. The temperature control device 260 may be a thermoelectric cooler, such as a Peltier device, for cooling the array of lasers 226-1 to 226-n and the AWG 225. In this embodiment, the AWG tray 242 supports the AWG 225 above the lasers 226-1 to 226-n. By using the same temperature control device and supporting the AWG 225 above the lasers 226-1 to 226-n, a desired temperature range can be maintained with relatively low power consumption and within a relatively small space.

In the illustrated embodiment, the AWG tray 242 includes a supporting portion 244 that supports the AWG 225 and side portions 246, 248 that hold the supporting portion 244 above the lasers 226-1 to 226-n. The laser array tray 240 may be a relatively flat plate that fits between the side portions 246, 248 such that both the laser array tray 240 and the side portions 246, 248 of the AWG tray 242 are separately thermally coupled to the temperature control device 260 (e.g., to the cold side of a TEC). The laser array tray 240 and the side portions 246, 248 of the AWG tray 242 may each directly contact the temperature control device 260 or may be thermally coupled through another thermally conductive material. Because a larger surface area of the laser array tray 240 is thermally coupled to the temperature control device 260, the temperature of the lasers 226-1 to 226-n may be controlled more precisely. Although the illustrated embodiment shows a particular shape for the trays 240, 242, other shapes and configurations may also be used to support the lasers 226-1 to 226-n and the AWG 225 and to provide thermal coupling to the same temperature control device 260. Each of the trays 240, 242 may also be formed as one piece or multiple pieces. Other embodiments of a multi-channel TOSA may also use different structures to support the lasers and/or AWG.

Both of the trays 240, 242 may be made of a thermally conductive material having a thermal conductivity greater than 60 W/(m·K) and more specifically greater than 80 W/(m·K). The trays 240, 242 may be made, for example of copper or zinc. At least a portion of the trays 240, 242 may also be gold plated, for example, to facilitate soldering to the trays 240, 242. In one example, the laser array tray 240 is made of AlN with a thermal conductivity of about 170 W/(m·K) and the AWG tray 242 is made of copper with Au plating and having a thermal conductivity of greater than 300 W/(m·K).

To provide thermal isolation in this embodiment, the multi-channel TOSA 220 also includes a thermal isolation bar 270 for providing electrical connections between the lasers 226-1 to 226-n (and/or other components) and external circuitry. The thermal isolation bar 270 is thermally coupled to the temperature control device 260 (e.g., to the cold side of a TEC) to prevent heat from being conducted to the lasers 226-1 to 226-n. In particular, the thermal isolation bar 270 may directly contact the temperature control device 260 or may contact the laser array tray 240. In the illustrated embodiment, the thermal isolation bar 270 extends across the array of lasers 226-1 to 226-n from one side to the other side of the TOSA 220. In other embodiments, the thermal isolation bar 270 may include multiple sections and/or may extend across only a portion of the TOSA 220. Each of the lasers 226 (and/or other optoelectronic components) is wire bonded with at least one wire 272 to a conductive pad 271 on the thermal isolation bar 270. Although a single laser 226 is shown with a single wire 272, multiple wires 272 may be used to wire bond each of the lasers (e.g., lasers 226-1 to 226-n shown in FIG. 4) to separate conductive pads on the thermal isolation bar 270. Although the thermal isolation bar 270 is shown having a rectangular shape, other shapes and configurations are possible.

The thermal isolation bar 270 provides an electrical connection between the lasers 226 and external circuitry, such as the printed circuit board 208. As shown, for example, the thermal isolation bar 270 is wire bonded with wires 274 to conductive pads 280 located on a TOSA housing portion 282. The conductive pads 280 are electrically connected to circuitry, for example, via conductive traces or paths 284 extending through the housing portion 282 and via the conductive leads 224 (see FIG. 5). Multiple wires 274 may be used between respective conductive pads 271 on the thermal isolation bar 270 and the conductive pads 280 on the housing portion 282 to provide multiple electrical connections between each of the lasers in a laser array and the circuitry. Although a specific arrangement providing an electrical connection to external circuitry is illustrated and described, other arrangements may also provide an electrical connection to the circuitry.

Because the thermal isolation bar 270 is thermally coupled to the temperature control device 260, the temperature of the thermal isolation bar 270 may be controlled (e.g., by cooling or heating) to prevent heat from being conducted from the pads 280, which are linked to the external environment, to the lasers 226. The thermal isolation bar 270 thus isolates the lasers 226 from the external heat generated in the environment external to the TOSA 220 while allowing the lasers 226 to be electrically connected to circuitry outside of the TOSA 220. The thermal isolation bar 270 may be made of a thermally conductive material having a thermal conductivity greater than 60 W/(m·K), such as, for example, aluminum nitride (AlN). The conductive traces or paths on the thermal isolation bar 270 may include gold, for example, to facilitate solderability.

As shown in greater detail in FIG. 6, each laser 226 may be provided as a heated laser package 600 that includes and is thermally shielded by a laser thermal shield 250 defining a thermally shielded compartment 252. In this embodiment, the laser thermal shield 250 includes walls 251 extending from a base 253 to define the thermally shielded compartment 251. The laser thermal shield 250 is thermally coupled to the temperature control device 260, for example, via the laser tray 240 (see FIG. 4). The temperature control device 260 may thus maintain a consistent temperature (e.g., 40° C.) of the laser thermal shield 250 such that the walls 251 of the thermal shield 250 thermally shield the laser 226 from heat within the TOSA (e.g., from other lasers and/or from thermal air flow in the TOSA). Although a single thermal shield 250 is shown thermally shielding a single laser 226, a plurality of thermal shields may be used to thermally shield the respective lasers 226-1 to 226-n in the laser array.

The laser array thermal shield 250 may be made of a thermally conductive material having a thermal conductivity greater than 60 W/(m·K) and more specifically greater than 80 W/(m·K) and, for example, about 160 W/(m·K). The laser array thermal shield 440 may be made, for example, from copper tungsten and may also be gold plated, for example, to facilitate soldering. Other thermally conductive materials may also be used.

As shown, the laser package 600 may include a laser diode chip 227 (e.g., a DFB laser diode chip) mounted on a sub-mount 229. The thermally shielded compartment 252 is configured to receive the sub-mount 229 between the walls 251. A monitor photodiode 228 may also be mounted on the sub-mount 229, for example, to monitor light emitted from the laser diode chip 227. A heating resistor 264 may be located adjacent the laser diode chip 227 to provide independent control of the temperature of the laser diode chip 227 and thus the wavelength of the emitted laser light. A transistor (not shown in FIG. 6) may also be located in proximity to the laser diode chip 227 and electrically coupled to the heating resistor 264. The transistor may be configured to control drive current to the heating resistor to control the thermal level of the resistor based on a temperature control signal, for example as may be provided by temperature control device 260 or any suitable temperature control processor. The location of the transistor, within the laser package 600 and in proximity to the laser diode, may allow additional heat that is generated by the transistor to be transferred to the laser diode 227.

During operation, for example, the temperature control device 260 may be used to establish a consistent global temperature of the array of lasers 226-1 to 226-n and the heating resistors 264 (and associated transistors) may be used to raise the local temperature of each of the lasers 226 individually and independently above this global temperature to change the wavelength, as will be described in greater detail below. The thermal shield 250 facilitates this independent temperature control of each of the lasers by preventing heat from outside of the thermally shielded compartment 252 from affecting the laser diode chip 227.

The illustrated embodiment of the laser thermal shield 250 is also configured to receive a lens 223, for example, to focus emitted laser light into an optical fiber or waveguide. As shown, the laser thermal shield 250 also receives and supports the lens such that the laser diode chip 227 is aligned with the lens 223. Although the illustrated embodiment shows the laser thermal shield 250 with a particular shape, other shapes and configurations are also possible. In other embodiments, for example, the laser thermal shield 250 may be closed at the top.

Referring to FIGS. 7 and 7A, a system and method of controlling temperature for tuning channel wavelengths in a temperature controlled multi-channel TOSA 720 is described in greater detail. The temperature controlled multi-channel TOSA 720 generally includes an array of lasers 726-1 to 726-n and an optical multiplexer 725 that combines the laser light emitted from the lasers 726-1 to 726-n at the channel wavelengths. The lasers 726-1 to 726-n may include thermally tunable DFB laser diodes with a wavelength drift of about 0.1 nm/° C. and the optical multiplexer 725 may include an AWG. In one embodiment, the TOSA 720 may include 16 lasers 726-1 to 726-n to provide 16 channels, although other embodiments may include other numbers of lasers.

A global temperature T₁ is established for the array of lasers 726-1 to 726-n such that at least one of the lasers (e.g., laser 726-1 or L₁) is tuned to one of the channel wavelengths (e.g., λ₁) at the global temperature T₁. The channel wavelength λ₁ that is tuned at the global temperature T₁ may be, for example, the closest ITU channel. At the global temperature T₁, the other lasers (e.g., laser 726-2 to 726-n or L₂ . . . L_(n)) may emit wavelengths that are shorter than the other respective channel wavelengths. Thus, the local temperatures (e.g., T₂ . . . L) of the other individual lasers (e.g., laser 726-2 to 726-n or L₂ . . . L_(n)) may be raised above the global temperature T₁ to fine tune the other lasers to the other channel wavelengths (e.g., λ₁ . . . λ_(n)). In some embodiments, these local temperatures (e.g., T2 . . . Tn) may be adjusted by varying the drive currents to heating resistors adjacent to the laser diodes. The drive currents may be obtained from calibration lookup tables associated with the laser diodes. In some embodiments, these local temperatures (e.g., T₂ . . . T_(n)) may be adjusted in response to monitored wavelengths associated with these other lasers (e.g., laser 726-2 to 726-n) such that the lasers remain tuned to the channel wavelengths (e.g., λ₁ . . . λ_(n)).

As shown in FIG. 7, a temperature control device 760, such as a TEC, is thermally coupled to the array of lasers 726-1 to 726-n to establish the global temperature T₁. For example, the temperature control device 760 may cool the array of lasers 726-1 to 726-n to establish the global temperature T₁. Individual heaters 764-1 to 764-n, such as resistors and transistors, are located adjacent the respective lasers 726-1 to 726-n to raise the local temperatures of the lasers above the global temperature established by the temperature control device 760. Although the illustrated embodiment shows a heater 764-1 adjacent the laser 726-1, this heater 764-1 may not be needed if this laser 726-1 remains tuned at the channel wavelength λ₁ as a result of the global temperature T₁ established by the temperature control device 760.

The temperature controlled multi-channel TOSA 720 further includes a temperature wavelength control system 766 for controlling the temperature control device 760 and heaters 764-1 to 764-n. The temperature wavelength control system 766 may be implemented, for example, using any combination of hardware, software and firmware (including calibration look up tables) and may be located on a circuit board located in the TOSA (e.g., printed circuit board 208 shown in FIG. 2). The temperature wavelength control system 766 may include a global temperature control 768 for controlling the global temperature and a local temperature control 769 for controlling the local temperatures.

The global temperature control 768 controls the global temperature established by the temperature control device 760 in response to a monitored temperature obtained, for example, from a sensor 767 such as a thermistor. In particular, the global temperature control 768 may receive a global temperature signal indicative of a monitored global temperature from the sensor 767 and may compare the monitored global temperature with a target global temperature. The global temperature control 768 may then provide a control signal to the temperature control device 760 to raise or lower the monitored global in a feedback control loop. The sensor 767 may be located on the temperature control device 760 or in any other location capable of sensing the global temperature T₁ established for the array of lasers 726-1 to 726-n (e.g., on a baseplate coupled to the TEC or on the laser array tray 240 shown in FIG. 5). Other techniques for establishing the global temperature may also be used.

The local temperature control 769 controls the local temperature established by each of the heaters 764-1 to 764-n in response to monitored wavelengths obtained, for example, from a wavelength meter 790. The wavelength meter 790 may be located outside of the TOSA 720. A demultiplexer (not shown) may demultiplex the combined WDM optical signal 710 transmitted by the TOSA 720 and the wavelength meter 790 monitors the respective wavelengths of the demultiplexed channels associated with the respective lasers. The local temperature control 769 may then provide local temperature control signals to the respective heaters (e.g., 764-2 to 764-n), in response to the monitored wavelengths, to raise or lower the local temperatures such that the lasers (e.g., 726-2 to 726-n) remain tuned to the respective channel wavelengths.

Where the heaters 764-1 to 764-n are resistors, for example, the local temperature control signals may be the current supplied to the resistors, which may be adjusted to adjust the heat provided by the resistors and thus the local temperatures. In one embodiment, the local temperature control 769 receives monitored wavelength data representative of the monitored wavelengths and compares the monitored wavelengths to target channel wavelengths. In other embodiments, the comparison of the monitored wavelengths and the target channel wavelengths may occur outside of the TOSA 720 and the local temperature control 769 may receive a signal that indicates whether or not to raise or lower the local temperatures, respectively.

According to one example, the wavelengths may be initially tested by the wavelength meter 790 for all of the channels to determine which of the channels is closest to an ITU channel. The global temperature may then be determined such that the laser (e.g., laser 726-1) closest to the ITU channel is tuned to that channel at the global temperature T₁. The resistor currents may also be determined for each of the resistor heaters to provide the local temperatures T₂ . . . T_(n) that will tune the other lasers (e.g., lasers 726-2 to 726-n) to the other channel wavelengths. During operation of the TOSA according to this example, the TEC is then turned on and set to the determined global temperature, and the heater resistors are provided with the resistor currents determined to provide the local temperatures. The wavelength meter 790 then monitors the wavelengths, and the local temperature control 769 adjusts the resistor currents in response to the monitored wavelengths to maintain the lasers tuned to the respective channel wavelengths.

Referring to FIG. 8, an embodiment of a system for controlling the local temperature of a laser diode 227 is shown. The heated laser package 600 is shown to include a transistor 806, a heating resistor 808 and a laser diode 227. The transistor 806, which is coupled between a supply voltage source and the heating resistor 808, may be configured to control the drive current, I, through the heating resistor 808. Transistor 806 may be any suitable type of transistor, such as, for example, a bipolar junction transistor (BJT) or a metal oxide semiconductor field effect transistor (MOSFET). The drive current may vary between zero amperes and a maximum current, Imax, depending on the temperature control signal (e.g., voltage) applied to the base (or gate) of transistor 806, where higher drive currents result in greater heat generation.

The temperature control voltage may be generated by a processor 804, or any other suitable circuit including, for example, the local temperature controller 769. Processor 804 may be located on the PCB 208 or at any other suitable location, typically external to the laser package 600, for example on the OLT 110 or ONU 112. In some embodiments, processor 804 may be configured to access a look up table 802 which stores calibration data that provides a link or cross reference between drive currents (or equivalent temperature control voltages) and associated optical wavelengths generated by laser diode 227.

The transistor 806 and resistor 808 may be located in close enough proximity to laser diode 227 such that a desired level of heat transfer efficiency is enabled between the components. If transistor 806 were located external to laser package 600 (e.g., outside the thermal shield), any heat generated by the transistor would largely be wasted and would represent a drain on the overall power budget of the system. Because transistor 806 is located on (or otherwise incorporated into) the heated laser package 600, the heat generated by the transistor may be utilized, at least in part, as an additional thermal source (i.e., in addition to the heat generated by resistor 808) to improve the power efficiency of the system.

The following example illustrates power consumption for a case where the supply voltage is 3.3 volts, the heating resistor is 20 ohms and the temperature control voltage is set to 2.1 volts. In this case the drive current I, which equals

(temperature control voltage−transistor bias voltage)/R=(2.1−0.7)/20=70 mA,

generates heat in the resistor equal to I²R=0.07*0.07*20=98 mW. The total power consumed by the heating circuit, however, is Vsupply*I=3.3*0.07=231 mW. In this example (i.e., at this temperature control voltage point) a significant fraction of the total power consumed by the heating circuit is associated with the transistor which may be in the form of heat dissipation from the transistor. By locating the transistor 806 within the heated laser package 600 in proximity to the laser diode 227, a portion of this heat dissipation may be applied towards regulation of the local temperature of the laser diode to adjust or maintain the laser wavelength. This allows for a decrease in the overall power consumption of the heating circuit and relaxes the power budget constraints of the system.

Referring to FIG. 9, a flowchart of operations 900 illustrates a method for controlling the local temperature of a laser diode 227 consistent with another embodiment of the present disclosure. At operation 910, a drive current is determined for a heating resistor. The drive current is selected to correspond to a local temperature generated by the heating resistor, such that the local temperature is associated with a desired channel wavelength. The heating resistor is adjacent to the laser in a laser package. At operation 920, the drive current is generated by applying a temperature control voltage to a transistor that is coupled between a supply voltage and the heating resistor. The transistor is configured to regulate the drive current based on the temperature control voltage and the transistor is also incorporated in the laser package to enable heat from the transistor to transfer to the laser diode in addition to the heat provided by the heating resistor.

Although the exemplary embodiments include a multi-channel TOSA, the heated laser package and the system and method for controlling the local temperature of the laser diode in the heated laser package may also be used in other types of optical transmitters.

Consistent with an embodiment, a temperature controlled multi-channel transmitter optical subassembly (TOSA) includes a TOSA housing, a printed circuit board (PCB) comprising a laser driver and a temperature control circuit, the PCB located in the TOSA housing, and an array of laser packages coupled to the PCB. Each of the laser packages includes a laser diode configured to generate laser light from power provided by the laser driver. The laser light is associated with a respective optical channel and the laser diode is thermally tunable to a channel wavelength associated with the respective optical channel. The laser package also includes a heating resistor located proximate to the laser diode, the heating resistor configured to raise a local temperature of the laser diode above a global temperature of the TOSA to thermally tune the laser diode. The laser package further includes a transistor configured to adjust a drive current through the heating resistor, the drive current based on a temperature control signal provided by the temperature control circuit, wherein additional heat generated by the transistor is transferred, at least in part, to the laser diode to further raise the local temperature of the laser diode.

Consistent with another embodiment, a heated laser package includes a laser diode configured to generate laser light from power provided by a laser driver. The laser light is associated with a respective optical channel and the laser diode is thermally tunable to a channel wavelength or band of channel wavelengths associated with the respective optical channel. The heated laser package also includes a heating resistor located proximate to the laser diode and configured to raise a local temperature of the laser diode to thermally tune the laser diode. The heated laser package further includes a transistor configured to adjust a drive current through the heating resistor based on a temperature control signal. Additional heat generated by the transistor is transferred, at least in part, to the laser diode to further raise the local temperature of the laser diode.

Consistent with a further embodiment, a multi-channel transceiver module includes a transceiver housing and at least one temperature controlled multi-channel transmitter optical subassembly (TOSA) located in the transceiver housing. The TOSA is configured to transmit a wavelength division multiplexed (WDM) optical signal on multiple channel wavelengths. The TOSA includes a printed circuit board (PCB) comprising a laser driver and a temperature control circuit, the PCB located in the TOSA housing. The TOSA also includes an array of laser packages coupled to the PCB. The laser packages include a laser diode configured to generate laser light from power provided by the laser driver, the laser light associated with a respective optical channel and the laser diode thermally tunable to a channel wavelength associated with the respective optical channel. The laser packages also include a heating resistor located proximate to the laser diode, the heating resistor configured to raise a local temperature of the laser diode above a global temperature of the TOSA to thermally tune the laser diode. The laser packages further include a transistor configured to adjust a drive current through the heating resistor, the drive current based on a temperature control signal provided by the temperature control circuit, wherein additional heat generated by the transistor is transferred, at least in part, to the laser diode to further raise the local temperature of the laser diode. The TOSA further includes an optical multiplexer optically coupled to the array of laser packages, the optical multiplexer configured to combine the laser light at different respective channel wavelengths. The multi-channel transceiver module also includes at least one multi-channel receiver optical subassembly (ROSA) located in the transceiver housing, the ROSA configured to receive a wavelength division multiplexed (WDM) optical signal on multiple channel wavelengths.

Consistent with yet another embodiment, a method for controlling temperature for individually tuning lasers in a laser array to a plurality of channel wavelengths includes determining a drive current for a heating resistor, wherein the drive current corresponds to a local temperature generated by the heating resistor. The local temperature is associated with one of the channel wavelengths and the heating resistor is adjacent to the laser in a laser package. The method further includes generating the drive current by applying a temperature control voltage to a transistor. The transistor is coupled between a supply voltage and the heating resistor and the transistor is configured to regulate the drive current based on the temperature control voltage. The transistor is incorporated in the laser package.

While the principles of the invention have been described herein, it is to be understood by those skilled in the art that this description is made only by way of example and not as a limitation as to the scope of the invention. Other embodiments are contemplated within the scope of the present invention in addition to the exemplary embodiments shown and described herein. Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention, which is not to be limited except by the following claims. 

What is claimed is:
 1. A temperature controlled multi-channel transmitter optical subassembly (TOSA) comprising: a TOSA housing; a printed circuit board (PCB) comprising a laser driver and a temperature control circuit, said PCB located in said TOSA housing; and an array of laser packages coupled to said PCB, each of said laser packages comprising: a laser diode configured to generate laser light from power provided by said laser driver, said laser light associated with a respective optical channel and said laser diode thermally tunable to a channel wavelength associated with said respective optical channel; a heating resistor located proximate to said laser diode, said heating resistor configured to raise a local temperature of said laser diode above a global temperature of said TOSA to thermally tune said laser diode; and a transistor configured to adjust a drive current through said heating resistor, said drive current based on a temperature control signal provided by said temperature control circuit, wherein additional heat generated by said transistor is transferred, at least in part, to said laser diode to further raise said local temperature of said laser diode.
 2. The temperature controlled multi-channel TOSA of claim 1, wherein said temperature control circuit is further configured to generate said temperature control signal based on a calibration look up table associated with said laser diode.
 3. The temperature controlled multi-channel TOSA of claim 1, wherein said laser diode is a distributed feedback (DFB) laser.
 4. The temperature controlled multi-channel TOSA of claim 1, wherein said channel wavelengths include ITU channels wavelengths.
 5. The temperature controlled multi-channel TOSA of claim 1, further comprising a temperature control device located in said TOSA housing and thermally coupled to said array of laser packages for establishing said global temperature for said array of laser packages such that at least one laser diode in said array of laser packages is tuned to at least one of said channel wavelengths at said global temperature.
 6. The temperature controlled multi-channel TOSA of claim 5, wherein said temperature control device is a thermoelectric cooler.
 7. The temperature controlled multi-channel TOSA of claim 5, further comprising: a plurality of laser thermal shields for thermally shielding said array of laser packages, said laser thermal shields being thermally coupled to said temperature control device and defining a plurality of thermally shielded compartments, wherein each of said thermally shielded compartments receives and thermally shields a respective one of said laser packages while allowing emitted laser light to pass out of said shielded compartments, and wherein said heating resistors and transistors are located in respective ones of said thermally shielded compartments.
 8. The temperature controlled multi-channel TOSA of claim 5, wherein the one of said channel wavelengths tuned at said global temperature is the smallest of the channel wavelengths.
 9. The temperature controlled multi-channel TOSA of claim 1, further comprising a wavelength monitor located outside of said TOSA, said wavelength monitor configured to generate monitored wavelength data, and wherein said temperature control circuit is further configured to receive said monitored wavelength data and adjust said temperature control signal based on said monitored wavelength data.
 10. A heated laser package comprising: a laser diode configured to generate laser light from power provided by a laser driver, said laser light associated with a respective optical channel and said laser diode thermally tunable to a channel wavelength or band of channel wavelengths associated with said respective optical channel; a heating resistor located proximate to said laser diode, said heating resistor configured to raise a local temperature of said laser diode to thermally tune said laser diode; and a transistor configured to adjust a drive current through said heating resistor, said drive current based on a temperature control signal, wherein additional heat generated by said transistor is transferred, at least in part, to said laser diode to further raise said local temperature of said laser diode.
 11. The heated laser package of claim 10 further comprising a submount, wherein said laser diode, said heating resistor, and said transistor are mounted on said submount.
 12. The heated laser package of claim 11 further comprising a laser array thermal shield defining a thermally shielded compartment, and wherein said submount with said laser diode, said heating resistor, and said transistor are located within said thermally shielded compartment.
 13. A multi-channel transceiver module comprising: a transceiver housing; at least one temperature controlled multi-channel transmitter optical subassembly (TOSA) located in said transceiver housing, the TOSA being configured to transmit a wavelength division multiplexed (WDM) optical signal on multiple channel wavelengths, said TOSA comprising: a printed circuit board (PCB) comprising a laser driver and a temperature control circuit, said PCB located in said TOSA housing; and an array of laser packages coupled to said PCB, each of said laser packages comprising: a laser diode configured to generate laser light from power provided by said laser driver, said laser light associated with a respective optical channel and said laser diode thermally tunable to a channel wavelength associated with said respective optical channel; a heating resistor located proximate to said laser diode, said heating resistor configured to raise a local temperature of said laser diode above a global temperature of said TOSA to thermally tune said laser diode; and a transistor configured to adjust a drive current through said heating resistor, said drive current based on a temperature control signal provided by said temperature control circuit, wherein additional heat generated by said transistor is transferred, at least in part, to said laser diode to further raise said local temperature of said laser diode; and an optical multiplexer optically coupled to said array of laser packages, said optical multiplexer configured to combine said laser light at different respective channel wavelengths; and at least one multi-channel receiver optical subassembly (ROSA) located in said transceiver housing, said ROSA configured to receive a wavelength division multiplexed (WDM) optical signal on multiple channel wavelengths.
 14. The temperature controlled multi-channel transceiver module of claim 13, wherein said temperature control circuit is further configured to generate said temperature control signal based on a calibration look up table associated with said laser diode.
 15. The temperature controlled multi-channel transceiver module of claim 13, further comprising a temperature control device located in said transceiver housing and thermally coupled to said array of laser packages for establishing said global temperature for said array of laser packages such that at least one laser diode in said array of laser packages is tuned to at least one of said channel wavelengths at said global temperature.
 16. The temperature controlled multi-channel transceiver module of claim 13, wherein said temperature control device is a thermoelectric cooler.
 17. A method for controlling temperature for individually tuning lasers in a laser array to a plurality of channel wavelengths, the method comprising: determining a drive current for a heating resistor, wherein said drive current corresponds to a local temperature generated by said heating resistor, said local temperature associated with one of said channel wavelengths, and wherein said heating resistor is adjacent to said laser in a laser package; generating said drive current by applying a temperature control voltage to a transistor, wherein said transistor is coupled between a supply voltage and said heating resistor and said transistor is configured to regulate said drive current based on said temperature control voltage, and wherein said transistor is incorporated in said laser package.
 18. The method of claim 17, wherein said heating resistor drive current is obtained from a calibration look up table associated with said laser.
 19. The method of claim 17, wherein said temperature control voltage is obtained from a calibration look up table associated with said laser.
 20. The method of claim 17, further comprising: establishing a global temperature for said laser array such that at least one laser in said laser array is tuned to one of said channel wavelengths at said global temperature; and raising said local temperatures for other lasers in said laser array individually above said global temperature such that said other lasers are tuned to said other channel wavelengths, respectively, said local temperatures raised by said heating resistor.
 21. The method of claim 17, further comprising: monitoring said wavelengths associated with each of said lasers; and adjusting said local temperatures of said other lasers in response to monitored wavelengths to maintain said other lasers tuned to said other channel wavelengths.
 22. The method of claim 17, wherein said channel wavelengths include ITU channels wavelengths. 